Nebulizer solution dilution

Question

For an adult inhalation preparation, a pharmacist requests 8 mL of 10% acetylcysteine using 20% stock and a labeled diluent. How many mL of stock should the pharmacy technician measure?

1. A0.4 mL✗ Incorrect

   Incorrect. This answer misplaces the decimal point (10 times too little).

2. B4 mL✓ Correct

   Correct. C1 × V1 = C2 × V2 → V1 = 10 × 8 ÷ 20 = 4 mL of stock.

3. C16 mL✗ Incorrect

   Incorrect. This answer inverts the concentrations.

4. D40 mL✗ Incorrect

   Incorrect. This answer misplaces the decimal point (10 times too much).

Answer

B. 4 mL

Rationale

The inhalation label permits the stronger solution to be diluted. The requested volume is the entire mixture, not the amount of stock alone.

Worked solution: C1 × V1 = C2 × V2 → V1 = 10 × 8 ÷ 20 = 4 mL of stock.